Magnetic recording medium, method for manufacturing recording medium and magnetic recording apparatus

ABSTRACT

A magnetic recording layer is formed on an under-layer comprising a Cu crystalline grain layer and a deposited nitrogen atom layer on the Cu crystalline grain layer surface. Then the magnetic recording layer comprising very small average grain diameter and sharp grain diameter distribution is obtained. The magnetic recording medium comprising the magnetic recording layer shows excellent signal to noise ratio at high density recording.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/080,487, filed on Mar. 16, 2005, which is based upon and claims thebenefit of priority from the prior Japanese Patent Application No.2004-090669, filed on Mar. 25, 2004; the entire contents of both ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to magnetic recording media, methods formanufacturing recording media and magnetic recording apparatus, inparticular, to magnetic recording media having high recording density,methods for manufacturing the recording media and magnetic recordingapparatus such as hard disk drives in which the high-density recordingmedia are equipped.

2. Description of the Related Art

Hard disk drives (HDDs) have been expanding their application scope fromthe first computer related application to various other applications,such as home video recorder and car carrying navigation systemapplications as magnetic recording systems for recording and reproducinginformation. The expansion is due to their advantage such as high dataaccess speed and high data storage reliability in addition to their highrecording capacity, performance with low cost. Requirements for HDDshaving larger recording capacity have been increased with the expansionof the HDD application scope. Replying to the requirements, largecapacity recording technology has been advanced by increasing recordingdensity of the magnetic recording media.

With increasing recording density of the magnetic recording media ofHDDs, the recording bit sizes and the diameters for the magnetizationreversal units became very small. As the result, thermally decreasingphenomena of recorded signal magnetization and the recording andreproducing performance by thermal fluctuation effect caused by the verysmall magnetization reversal units became notable. Furthermore, noisesignals which appear at boundary regions between recording bits becamelarge as a result of decreasing recording bit to a very small size, andthe noise became to give a large influences upon the signal to noiseratio. Therefore, in order to attain further high recording density, itis required to stabilize thermal stability of the recorded signalmagnetization at one hand and to attain low noise characteristics athigh recording density at the other hand.

To decrease magnetic recording medium noise, size of magneticcrystalline grains constructing recording-layer have been made smallerup to now. For example, magnetic crystalline grains of Co—Crmagnetic-layer of widely used magnetic recording media were made smallby adding small amount of Ta or B (refer to Japanese Patent Laid-openApplications Nos. HEI 11-154321 and 2003-338029), and by precipitatingnonmagnetic Cr by heat treating at appropriate temperature (refer toJapanese Patent Laid-open Applications Nos. HEI 3-235218, and HEI6-259764). Recently, a method for obtaining magnetic recording layerhaving so called granular structure obtained by adding oxides such asSiO_(x) to the magnetic layer was applied. In the granular structuredmagnetic layer, nonmagnetic grain boundary material enclose magneticcrystalline grains (refer to Japanese Patent Laid-open Applications Nos.HEI 10-92637, and 2001-56922).

These methods, however, cannot control the crystalline grains of themagnetic-layer and the under-layer by going back to the nucleationprocesses for the crystalline grains of the under-layer and the magneticrecording layer. These methods control an average magnetic crystallinegrain diameter and grain boundary regions merely by choosing combinationof raw materials, the raw material composition, or by choosing ofdepositing conditions. When the crystalline grain diameters in theunder-layer are tried to make smaller, the crystalline quality andcrystal orientation degree of the grains in the under-layer aredegraded, and the degraded crystalline quality of the under-layer grainsgives influence upon the formation of magnetic crystalline grains.

Actually it was found that the magnetic-layer prepared using thisprocedure showed distributions of broad grain size and grain boundarywidth. Magnetic recording media decreasing the average grain size of themagnetic crystalline grains to 5 nm showed poor thermal fluctuationdurability. Very small grain diameter components unstable to thermalfluctuation were included at large fraction. Then it was difficult toattain further high recording density using this method.

SUMMARY

In order to attain high recording density of a magnetic recordingmedium, it is required to obtain recorded magnetization stability tothermal fluctuation and to attain low noise at high recording density.Then for obtaining higher recording density, it is required to solve twoproblems. One of the problems to be solved is to attain low noise bydecreasing average diameter of the magnetic crystalline grains in themagnetic-layer. The other problem to be solved is to attain thermalstability by obtaining small crystalline grain size distribution of themagnetic crystalline grains not including too small grains easilyinfluenced by thermal fluctuation.

As a result of long exploring work for obtaining a solution to theproblems, the inventors of the present invention have got a remarkablefinding. The finding is that the size of magnetic crystalline grains ofthe magnetic-layer can be made small with very sharp grain sizedistribution when the under-layer is a Cu metal film accompanied withthin deposited layer of nitrogen atoms. After carrying out a furtherinvestigation, the inventors could solve the problems described aboveand completed the present invention.

The magnetic recording medium of the present invention comprisessubstrate, an under-layer formed on the substrate, a magneticrecording-layer on the under-layer, and a protective-layer formed on themagnetic recording-layer. The under-layer comprises a grain diametercontrol under-layer comprising Cu crystalline grains and a depositedlayer of nitrogen atoms formed on the grain diameter controlunder-layer.

The method for producing magnetic recording medium of the presentinvention comprises a process for forming a grain diameter controlunder-layer comprising Cu crystalline grains on a substrate, a processfor forming a deposited layer of nitrogen atoms depositing nitrogen onthe grain diameter control under-layer surface, and a process forforming a magnetic recording-layer on the substrate having thenitrogen-layer deposited on a grain diameter control under-layer.

Furthermore, the magnetic recording and reproducing apparatus of thepresent invention comprises the magnetic recording medium describedabove, a recording medium driving mechanism, driving the magneticrecording medium, a recording and reproducing head mechanism, recordinginformation to the magnetic recording medium and reproducing from themagnetic recording medium, a head driving mechanism, driving therecording and reproducing head and a recording and reproducing signalprocessing system, processing recording signals and reproducing signals.

In the present invention, grain size of the under-layer crystalline Cuneed not be small. So the problem of prior art methods encountered forobtaining small magnetic grains using small grain size under-layers canbe avoided, and as the result, recording media having increasedrecording and reproducing characteristics can be obtained according tothe present invention. The Grain diameter control under-layer comprisingCu crystalline grains of the present invention can contain otherelements in a range in which the advantage of the present invention iseffective.

The detailed mechanism of obtaining small grain sizes by using nitrogendeposited Cu metal film-under-layer is not clear at present. Here, twopapers will be introduced and will give a concise comparison between thepresent invention and the papers.

In one of the papers appeared in Surface Science Vol. 523 pp 189-198(2003) an alternately arranged surface structure composed of regionshaving nitrogen absorption and regions having no absorption is reported.The nitrogen atoms were absorbed on bulk single crystal Cu surface aftercleaning up treatment in an ultra vacuum of 10⁻⁹ Pa.

In the other paper appeared in Material Science and Engineering Vol. 596pp. 169-177 (2002), an explanation for the ordered arrangement of thenitrogen atoms on the single crystal Cu surface is given. The orderedarrangement is explained as a self organizing structure due to an stressinteraction appeared on a clean surface of a bulk Cu single crystal.

Comparing the two papers with the present invention, it can be pointedout that the grain diameter control under-layer comprising Cucrystalline grains in the present invention is not a bulk single crystalbut a thin film. Therefore, the state having stress in the thin film ofthe present invention is quite different from the surfaces of bulk Cusingle crystals of these papers. Therefore, the re-oriented orderedsurface structure shown in these papers cannot always be expected forthe film of the present invention. At present, the mechanism of thepresent invention for obtaining small grain size is not clear. To findout the mechanism of the present invention is an important problem to besolved. According to the present invention, magnetic crystalline grainsof a magnetic-layer can be made small and magnetic recording media forhigh density recording with increased signal to noise ratio can beobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematically shown cross section view of a magneticrecording medium according to an embodiment of the present invention.

FIG. 2 is a schematically shown cross section view of a magneticrecording medium comprising an orientation control under-layercontrolling orientation of Cu crystalline grains between a substrate anda grain diameter control under-layer according to an embodiment of thepresent invention.

FIG. 3 is a schematically shown in-plane view of a magneticrecording-layer for a magnetic recording medium showing magneticcrystalline grains arranged in a form of a tetragonal lattice structureaccording to an embodiment of the present invention.

FIG. 4 is a schematically shown example of a ring pattern for thereciprocal lattice for the tetragonal lattice structure.

FIG. 5 is a schematically shown cross section view of a magneticrecording medium having an intermediate under-layer according to anembodiment of the present invention.

FIG. 6 is a schematically shown cross section view of a magneticrecording medium having a soft magnetic under-layer according to anembodiment of the present invention.

FIG. 7 is across section view of a magnetic recording medium having abiasing layer for a soft magnetic under-layer according to an embodimentof the present invention.

FIG. 8 is a schematically shown oblique view of a magnetic recordingapparatus according to an embodiment of the present invention showingthe construction by partially removing the covers.

FIG. 9 is a graph showing the relation between the number of depositednitrogen atoms per unit area and the average grain diameter of themagnetic recording-layer of Example 1.

FIG. 10 is a graph showing the relation between the average diameter ofthe Cu grains and the average diameter of the magnetic crystallinegrains in the magnetic recording-layer.

FIG. 11 is a graph showing the relation between the number of themagnetic crystalline grains per unit area of the magneticrecording-layer and signal to noise ratio of differential wave form(SNR_(m)) of the magnetic recording-layer of Example 1.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the drawings.

FIG. 1 is a schematically shown cross section view of a magneticrecording medium according to an embodiment of the present invention. Agrain diameter controlling Cu thin film under-layer 12 a is disposed ona substrate 11 in FIG. 1. A deposited layer of nitrogen atoms 12 b isformed on the diameter control under-layer 12 a. A magneticrecording-layer 14 is formed on the deposited layer of nitrogen atoms 12b, and a protective and lubricant layer 15 is formed on the magneticrecording-layer 14.

Quantity of the deposited nitrogen atoms per unit area desirable for thedeposited layer of nitrogen atoms 12 b on the surface of the graindiameter control under-layer 12 a is in a range from 1×10¹³ atoms/cm² to1×10¹⁵ atoms/cm², being expressed by the average number of atoms perunit area . . . . When the quantity is less than 1×10¹³ atoms/cm²,significant average grain diameter decreasing effect cannot be obtainedat the magnetic recording-layer. Furthermore, experimental result showsthat magnetic crystalline grain orientation of the magneticrecording-layer decreases when the quantity is larger than 1×10¹⁵atoms/cm². The quantity of the deposited nitrogen atoms is moredesirable to be in a range from 5×10¹³ atoms/cm² to 5×10¹⁴ atoms/cm².

Number of nitrogen atoms at the deposited layer of nitrogen atoms 12 bcan be evaluated by a secondly ion mass spectroscopy (SIMS) method.Other methods, nuclear reactor analysis (NRA) using H⁺ or ¹²C,Rutherford back scattering, X-ray photoelectron spectroscopy (XPS), andAuger electron spectroscopy (AES), for example, can be used forevaluating the number of nitrogen atoms. Furthermore, atom probe methoddescribed in Applied Physics Letters Vol. 69 pp. 3095-3097 can be usedfor the evaluation.

As a means for depositing nitrogen atoms on the surface of graindiameter control under-layer 12 a, a method of exposing grain diametercontrol under-layer 12 a after deposition to nitrogen ions or nitrogenradicals can be used. Other methods of irradiating nitrogen ions to thegrain diameter control under-layer 12 a or sputtering the Cu surface innitrogen atmosphere can also be used. Furthermore, a method of exposingthe surface to NH₄ atmosphere and then removing H can be used.

The desirable Cu crystalline grains for the grain diameter controlunder-layer 12 a are grains having broader flat surface for obtainingthe magnetic recording layer 14 with better crystallinity. Accordingly,larger average grain diameter of the Cu grains is desirable. Thedesirable average grain diameter of the Cu grains is 50 nm or larger,and more desirable diameter is 100 nm or larger. A single crystal filmhaving no grain boundary is much more desirable. When the Cu film is noteven in a certain degree, the film can be available provided that thefilm has large fraction of terrace surfaces that form the film surface.

The grain diameter control under-layer 12 a in which the samecrystallographic plane of each Cu grain is oriented parallel to the sameplane is desirable because higher magnetic crystalline grain orientationcan be obtained in the magnetic recording-layer 14. The grain diametercontrol under-layer in which (100) plane of each Cu grain is orientedparallel to the substrate surface are especially desirable for obtainingsignificantly small magnetic crystalline grains in the magneticrecording-layer 14.

As shown in FIG. 2, an orientation control under-layer 12 c forincreasing (100) plane orientation of Cu grains in the grain diametercontrol under-layer 12 a can be placed between the substrate 11 andgrain diameter control under-layer 12 a. As the orientation controlunder-layer 12 c, at least one material selected from the groupconsisting essentially of NiAl, MnAl, MgO, NiO, TiN, Si, and Ge can beused. The orientation control under-layer 12 c need not be disposeddirectly adjacent to the grain diameter control under-layer 12 a and canbe disposed through an intervening layer.

The magnetic crystalline grains in the magnetic recording layer 14 areformed in plural per one Cu grain of the grain diameter control layer 12a on average. The desirable average areal density of the magneticcrystalline grains in the magnetic recording-layer 14 is in a range from1×10¹² grains/cm¹² to 8×10¹² grains/cm² for obtaining large reproducedoutput of the recorded signal. When the average a real density of themagnetic crystalline grains is less than 1×10¹² grains/cm², the SNRdecreases. The SNR decreases also when the average a real density isabove 8×10¹² grains/cm².

From experimental results by the present inventors, it has been foundthat noise level of recording and reproducing characteristics can bereduced substantially and is desirable when the magnetic crystallinegrains are arranged essentially in an ordered structure of tetragonallattice.

FIG. 3 schematically shows an in-plane structure of a magnetic recordingmedium according to an embodiment of the present invention. The whitesubjects express magnetic grains 1. Existence of tetragonal latticestructure arrangement of magnetic crystalline grains 1 can be evaluatedby image processing and analyzing transmission electron microscope (TEM)Figurers for the film plane of the magnetic recording-layer 14.

Using an image processing and analyzing software, a spectrum can beobtained as a result of a fast Fourier transformation of a binary Figureobtained by increasing contrast of a Figure for magnetic crystallinegrains and grain boundary regions. The magnetic crystalline grains canbe regarded to have an arrangement of tetragonal lattice structureessentially when patterns as shown in FIG. 4 can be recognized in thespectrum Practically, two types of periodical spots or rings having aratio of the distances to the center is 1:1/√2 (R₁ and R₁/√2 in FIG. 4).Similar evaluation can be performed using low energy electrondiffraction to the magnetic recording-layer and analyzing thediffraction patterns.

For the magnetic recording medium of the present invention, a magneticrecording-layer 14 having a granular structure is desirable. Thegranular structure with nonmagnetic grain boundary regions in themagnetic recording-layer 14 leads to a decrease in the exchangeinteraction between the magnetic crystalline grains and a significantdecrease in the transition noise of recording and reproducingcharacteristics.

Disordered alloys such as Co—Cr and Co—Pt, ordered alloys such as Fe—Pt,Co—Pt and Fe—Pd, and multi-layered films such as Co/Pt and Co/Pd aredesirable as materials for the magnetic recording-layer 14. These alloysand multi-layered films are desirable for their high crystallineanisotropy energy and therefore for their high thermal fluctuationdurability. Magnetic properties of these alloys and multi-layers can beimproved if necessary by adding some additive elements such as Cu, B,and Cr. CoCrPt, CoCrPtB, CoCrPtTa, CoCrPtNd, CoCrPtCu and FePtCu alloyscan be further desirably used as materials for the magneticrecording-layer 14.

As the materials for forming grain boundary regions of the granularstructure, compounds such as oxides and carbides are desirable, becausethese compounds do not form solid solution with the materials formingthe magnetic crystalline grains described above and can easily beseparated. Compounds such as SiO_(x), TiO_(x), CrO_(x), AlO_(x),MgO_(x), TaO_(x), Si_(x), TiC_(x), and TaC_(x) can be cited for formingthe grain boundary regions.

The magnetic recording-layer 14 can be double structure or multi-layeredstructure. In this case at least one of the-layers has the constructiondescribed above.

As shown in FIG. 5, an intermediate under-layer 12 d for controllingcharacteristics of magnetic recording-layer 14 can be disposed inaddition to the grain diameter control under-layer 12 a accompanied withdeposited nitrogen layer 12 b and the orientation control under-layer 12c.

The crystal orientation degree can be improved by using a granularstructured-layer as the intermediate under-layer 12 d. The recording andreproducing characteristics can be increased by the improved crystalorientation degree in addition to the smaller average grain size and thesmaller grain diameter distribution.

As the nonmagnetic crystalline materials of the intermediate under-layer12 d showing granular structure, Pt, Pd, Ir, Ag, Cu, Ru and Rh can becited. These metal materials are desirable because these metal materialsshow good lattice compatibility with magnetic crystalline grainsdescribed above and can improve crystal orientation degree.

As the materials for forming grain boundary regions of the intermediateunder-layer 12 d, compounds such as oxides and carbides are desirable.These compounds are desirable as the materials for forming grainboundary regions because these compounds do not form solid solution withthe nonmagnetic crystalline materials forming the magnetic crystallinegrains described above and can easily be separated. Compounds such asSiO_(x), TiO_(x), CrO_(x), AlO_(x), MgO_(x), TaO_(x), SiC_(x), TiC_(x),and TaC_(x) can be cited for forming the grain boundary regions. Thematerials constructing the under-layer can include magnetic metal whenthe under-layer is nonmagnetic as the whole.

The intermediate under-layer 12 d with a granular structure can beconstructed as multi-layer of two or more layers. The layer need not beplaced adjacent to the magnetic recording-layer 14.

The magnetic recording medium of the present invention is applied as aperpendicular magnetic recording medium when a soft magnetic under-layer16 is placed between the under-layers and the substrate 11 as shown inFIG. 6.

Disposing the soft magnetic under-layer 16 in the magnetic recordingmedium described above, so-called perpendicular double-layered medium,comprising the magnetic recording layer 14 disposed on the soft magneticlayer 16, can be constructed. The soft magnetic under-layer 16 shares apartial function of a magnetic head by returning magnetic flux inducedby the recording magnetic field from a single pole head passinghorizontally through the magnetic recording medium and turning back tothe magnetic head. Therefore, the soft magnetic under-layer 16 placed inthe magnetic recording medium plays a role for giving a sharpperpendicular magnetic field with sufficient magnitude to the magneticrecording layer 14.

As the soft magnetic under-layer 16, for example, CoZrNb, FeSiAl, FeTaC,CoTaC, NiFe, Fe, FeCoB, FeCoN and FeTaN, can be cited.

As shown in FIG. 7, a biasing-layer 17 consisted essentially of hardin-plane magnet-layer and antiferromagnetic material-layer, for example,can be disposed between the soft magnetic under-layer 16 and thesubstrate 11. Magnetic domains are easily formed in the soft magneticunder-layer 16, and magnetic domain walls induce spike like noise. Theformation of magnetic domains can be avoided by applying a magneticfield in one radial direction of the biasing-layer 17 and applyingbiasing field to the soft magnetic under-layer 16 placed on thebiasing-layer 17. The biasing-layer can be a multi-layered structurewith finely dispersed anisotropy field to avoid formation of largemagnetic domains.

As the material for constructing the biasing-layer 17, CoCrPt, CoCrPtB,CoCrPtTa, CoCrPtTaNd, CoSm, CoPt, FePt, CoPtO, CoPtCrO, CoPt—SiO₂,CoCrPt—SiO₂, and CoCrPtO—SiO₂ can be cited.

As shown in FIG. 6 and FIG. 7, the orientation control layer 12 cdescribed above can be disposed to improve (100) plane crystalorientation degree of Cu crystalline grains of grain diameter controlunder-layer 12 a.

Glass substrates, Al alloys substrates or Si single crystal substrateswith oxide surfaces, ceramic substrates, and plastic substrates can beused for the substrate 11. Furthermore, inorganic substrates plated withNiP, for example can be used.

Protective-layer 15 can be formed on the magnetic recording-layer 14. Asthe protective-layer 15, carbon or diamond like carbon can be used.Other materials SiN_(x), SiO_(x), and CN_(x) can be cited as theprotective-layer material.

As the method for depositing each-layer described above, vacuumevaporation method, every kind of sputtering method, molecular beamepitaxy method, ion beam evaporation method, laser abrasion method andchemical vapor deposition method can be used.

FIG. 8 is a schematically shown oblique view of a magnetic recordingapparatus according to an embodiment of the present invention showingthe construction by partially removing covers.

In FIG. 8, the magnetic disk 81 according to the present invention isattached to the spindle 82, and is driven at a constant rotating speedby a spindle motor not shown in the Figure. The slider 83 carrying arecording head for recording information and a MR head reproducing therecorded information for gaining access to the surface of the magneticdisk 81 is attached at the top of a suspension 84 constructed by a thinplate shaped flat spring. The suspension 84 is connected to one side ofan arm 85 having a bobbin holding a drive coil not shown in the Figure.

At the other side of the arm 85, a voice coil motor 86, a kind of linearmotor, is disposed. The voice coil motor 86 is constructed by a magneticcircuit composed of a drive coil rolled up to a bobbin of arm 85,permanent magnet and opposing yokes.

The arm 85 is supported by a ball bearing not shown in the Figure and isdriven to swing circularly by the voice coil motor 86. The position ofthe slider 83 on the magnetic disk 81 is controlled by the voice coilmotor 86. In the FIG. 8, a cover 88 is shown partially.

Hereinafter, examples of the present invention will be described toexplain the present invention further in detail.

EXAMPLE 1

Nonmagnetic 2.5 inches glass substrates were put into a vacuum chamberof an ANELVA Co. c-3010 type sputtering apparatus.

The vacuum chambers of the sputtering apparatus were evacuated to 1×10⁻⁶Pa or less. Then the substrates were heated using an infrared heater upto about 300° C. Keeping the substrate temperature to about 300° C.,about 200 nm CoZrNb film was deposited as a soft magnetic under-layer,and then an about 30 nm Cu film was deposited. The substrate temperaturewas then elevated to about 500° C., and nitrogen ions were irradiated tothe Cu film surface in 0.1 Pa nitrogen gas atmosphere using ion gun at200 eV. After the nitrogen ion irradiation, a 5 nm Fe₅₀Pt₅₀ film wasdeposited.

And then a 5 nm carbon film was deposited. For depositing CoZrNb film,Cu film, Fe₅₀Pt₅₀ film and C film, the Ar gas pressure was 0.7 Pa, 0.7Pa, 5 Pa and 0.7 Pa, respectively, and target material was CoZrNb, Cu,Fe₅₀Pt₅₀, and C, respectively. The sputtering was performed using DCsputtering.

Power inputted to the targets was fixed to 1,000 W for CoZrNb, Fe₅₀Pt₅₀and C deposition, and varied from in a range from 100 to 1,000 W for Cudeposition.

Then magnetic recording media having CO₅₀Pt₅₀, Fe₅₀Pd₅₀, andCo₇₀Cr₁₀Pt₁₀, instead of Fe₅₀Pt₅₀ were fabricated using almost the sameprocedure described above. The quantity of nitrogen deposition to the Cufilm surface was controlled choosing the ion irradiation time. Thecrystalline grain diameter of the Cu films was varied changing inputpower to the targets.

After finishing the deposition, each protective-layer was coated withabout 1.3 nm thick lubricant of perfluoropolyether (PFPE) by a dippingmethod. Then, various magnetic recording medium samples were obtained.

As a comparable example, conventional perpendicular magnetic recordingmedia were fabricated by the following procedure. Nonmagnetic 2.5 inchesglass substrates were put into the vacuum chambers of the sputteringapparatus and the vacuum chambers were evacuated to 1×10⁻⁶ Pa or less.After heating the substrate using an infrared heater up to about 300°C., 200 nm CoZrNb film as a soft magnetic under-layer, 10 nm Ta film asa seed-layer, 20 nm Ru film as a under-layer, 15 nmCO₆₅—Cr₂₀—Pt₁₄—Ta₁-layer as amagnetic recording-layer, and a 5 nmprotective-layer was deposited to each substrate, and then the lubricantwas coated using the procedure similar to the case for example describedabove. For depositing CoZrNb film, Ta film, Ru film and CoCrPtTa film,the Ar gas pressure was 0.7 Pa, 0.7 Pa, 0.7 Pa, 5 Pa and 0.7 Pa,respectively, and target material was CoZrNb, Ta, Ru and CO₆₅Cr₂₀Pt₁₄Ta₁, respectively. The sputtering was performed using DC sputtering.Power inputted to the targets was fixed to 1,000 W.

The microstructure, the crystalline grain diameters and the grain sizedistribution of each fabricated sample were evaluated by a transmissionelectron microscope (TEM) with accelerating voltage of 400 kV. Thequantity of nitrogen atoms deposited on the each Cu film was obtainedand confirmed by NRA using H⁺ method similar to the method descriptionfound in a report appeared at Surface Science Vol. 490 pp. 336-350, andSIMS method using Cs⁺.

Recording and reproducing characteristics (read write characteristics,R/W characteristics) of each magnetic recording medium was evaluated byusing a spin stand. The magnetic head applied was a combination of a 0.3μm track width single pole head and a 0.2 μm track width MR head.

The same measuring condition at a constant magnetic head position of 20min from the center and of 4,200 rpm the magnetic disk rotating speedwas applied.

Signal to noise ratio for derivative waveforms as an output of aderivative circuit (SNR_(m)) was measured and characterized as the SNRof each magnetic recording medium. The measured signal S was output forlinear recording density of 119 kfci, and the measured noise was rootmean square value at 716 kfci. In addition, the half width of thederivative waveforms (dPW₅₀) was evaluated to obtain as an index for theresolution of the recording.

Table 1 shows the average crystalline grain diameter d_(Mag) and thestandard deviation a of the magnetic-layer of each magnetic recordingmedium. TABLE 1 Average Magnetic diameter Standard Recording d_(Mag)deviation Layer (nm) σ(nm) Example 1-1 FePt 4.5 1.0 Example 1-2 CoCrPt4.3 1.0 Example 1-3 CoPt 4.8 1.1 Example 1-4 FePd 4.8 1.3 Comparative(conventional 7.1 2.5 Example 1 medium)

Comparing each magnetic recording medium of the Example 1 with themagnetic recording medium of the Comparative example 1 for the averagecrystalline grain diameter d_(Mag) and the standard deviation σ of themagnetic-layer in Table 1, each magnetic recording medium of the Example1 shows significantly smaller average crystalline grain diameter withsmaller standard deviation.

FIG. 9 shows a relationship between the quantity of deposited nitrogen θand the average magnetic crystalline grain diameter d_(Mag) for Fe₅₀Pt₅₀magnetic-layer obtained by a nuclear reaction analysis NRA. From thisFigure, it can be found that the crystalline grains are significantlysmall and are desirable

when the θ value is in a range from 1×10¹³ atom/cm² to 1×10¹⁵ atom/cm².Similar results were obtained for the cases of CO₅₀Pt₅₀, Fe₅₀Pd₅₀ andCo₇₀Cr₁₀Pt₂₀ magnetic-layer. For each magnetic recording medium, thenitrogen atoms deposited on the grain diameter control under-layercomprising Cu crystalline grains was detected by a chemical elementdistribution measurement using SMS toward the depth direction.

FIG. 10 shows a relationship between the average diameter of Cucrystalline grains at Cu-layer and the average diameter of magneticcrystalline grains for Fe₅₀Pd₅₀ magnetic-layers with 2×10¹⁴ atom/cm²deposited nitrogen. From FIG. 10, the average grain diameter of themagnetic-layer became significantly small when the average graindiameter of Cu-layer is 50 nm or larger.

FIG. 11 shows a relationship between SNR_(m) of each magnetic recordingmedium and number of magnetic crystalline grains per unit area (arealdensity of grains) n obtained by TEM observation for average diameter ofCu d_(Cu) of 100 μm. As seen from FIG. 11, the SNR_(m) increases anddesirable when the value of n is in a range from 1×10¹² grains/cm² to8×10¹² grains/cm². When the value of n was in a range from 1×10¹²grains/cm² to 8×10¹² grains/cm², plural number of magnetic grains of amagnetic recording medium is placed on a Cu crystalline grains onaverage.

Ordered arrangement of magnetic crystalline grains was investigated foreach in-plane TEM Figures using an image processing and analyzingsoftware “Image-Pro Plus” (Media Cybernetics Co., USA). To each TEMFigure, a modification was given to obtain a pattern expressed by binaryvariables by increasing the contrast between regions of the magneticcrystal grains and other regions. The Figure expressed by binary Figureswas then transformed by FFT. As the result, no ordered arrangement ofmagnetic grains in the magnetic-layer was recognized for theconventional medium. On the other hand, for each magnetic recordingmedium having n values in a range from 1×10¹² grains/cm² to 8×0¹²grains/cm², the ordered arrangement of the magnetic crystalline grainsto tetragonal lattice structure was recognized.

EXAMPLE 2

Nonmagnetic 2.5 inches glass substrates were put into the vacuumchambers and the vacuum chambers were evacuated to 1×10⁴ Pa or less.Then CoZrNb soft magnetic under-layer, Cu deposition and nitrogendeposition process were performed using the method described inExample 1. Then a 5 nm Fe₅₀Pt₅₀—SiO₂ magnetic-layer was formed using(Fe₅₀—Pt₅₀)-10 mol % SiO₂ composite target. Furthermore, magnetic diskshaving CO₅₀Pt₅₀, Fe₅₀Pd₅₀ and CO₇₀Cr₁₀Pt₂₀ respectively replacingFe₅₀Pt₅₀-layer of the disks in example 1 were fabricated usingrespective targets. Similarly, magnetic disks having TiO, Al₂O₃, TiC andTaC respectively, were fabricated replacing SiO₂-layer in Example 1.Then carbon protective-layer was deposited and lubricant-layer wascoated for each fabricated magnetic recording medium.

Table 2 shows SNR_(m) values and dPW₅₀ values for each magneticrecording medium. Magnetic recording media having magneticrecording-layer composite with the chemical compounds show increasedSNR_(m) and are desirable. For every film composite with chemicalcompounds, granular structure and essentially tetragonal arrangement ofthe magnetic crystalline grains of the magnetic-layer are recognized byTEM observation. TABLE 2 Magnetic Signal to half width recording noiseratio dPW₅₀ layer SNRm (dB) (nm) Example 2-1 FePt 17.1 98 Example 2-2CoCrPt 17.3 93 Example 2-3 CoPt 17.0 99 Example 2-4 FePd 16.8 97 Example2-5 FePt—SiO₂ 18.3 90 Example 2-6 CoCrPt—SiO₂ 18.6 89 Example 2-7CoPt—SiO₂ 18.0 90 Example 2-8 FePd—SiO₂ 18.0 89 Example 2-9 FePt—MgO18.2 91 Example 2-10 CoCrPt—MgO 18.2 90 Example 2-11 CoPt—MgO 18.0 87Example 2-12 FePd—MgO 17.8 86 Example 2-13 FePt—Al₂O₃ 17.9 89 Example2-14 CoCrPt—Al₂O₃ 17.9 86 Example 2-15 CoPt—Al2O₃ 17.7 87 Example 2-16FePd—Al2O₃ 17.7 89 Example 2-17 FePt—TiO 18.1 87 Example 2-18 CoCrPt—TiO18.2 90 Example 2-19 CoPt—TiO 17.9 87 Example 2-20 FePd—TiO 17.9 88Example 2-21 FePt—TiC 17.8 90 Example 2-22 CoCrPt—TiC 17.8 92 Example2-23 CoPt—TiC 17.7 90 Example 2-24 FePd—TiC 17.8 88 Example 2-25FePt—TaC 17.9 87 Example 2-26 CoCrPt—TaC 17.8 90 Example 2-27 CoPt—TaC17.8 87 Example 2-28 FePd—TaC 17.8 88 Comparative (conventional medium)15.4 109 Example 2

EXAMPLE 3

2.5 inch hard disk shaped nonmagnetic glass substrates were prepared andfilm depositions were performed using the process of Example 1 up tonitrogen deposition treatment. Then 10 nm Pt—SiO₂ layer was depositedusing Pt-10 mol % SiO₂ composite target. On the Pt—SiO₂-layer, variousmagnetic recording-layers were deposited and then various magneticrecording media were obtained after depositing carbon protective-layerand coating lubricant-layer using the procedure described in Example 2.In addition, magnetic recording media having Pd, Ir, Ag, Cu, Ru and Rhunder-layer, respectively, instead of the Pt under-layer, and magneticrecording media having TiO, Al₂O₃, MgO, TiC and TaC under-layer,respectively, instead of the SiO₂ under-layer were obtained usingrespective composite targets.

Table 3 shows SNR_(m) and dPW₅₀ for each magnetic recording mediumhaving CoCrPt—SiO₂ magnetic recording-layer and various under-layers.TABLE 3 signal to half width noise ratio dPW₅₀ Under layer SNRm (dB)(nm) Example 3-1 Pt—SiO₂ 19.6 80 Example 3-2 Pd—SiO₂ 19.6 81 Example 3-3Ir—SiO₂ 19.3 79 Example 3-4 Ag—SiO₂ 19.0 78 Example 3-5 Cu—SiO₂ 18.9 79Example 3-6 Ru—SiO₂ 19.8 77 Example 3-7 Rh—SiO₂ 19.7 77 Example 3-8Pt—MgO 19.4 81 Example 3-9 Pd—MgO 19.4 80 Example 3-10 Ir—MgO 19.0 77Example 3-11 Ag—MgO 19.0 81 Example 3-12 Cu—MgO 19.3 81 Example 3-13Ru—MgO 19.5 79 Example 3-14 Rh—MgO 19.5 77 Example 3-15 Pt—Al₂O₃ 19.4 77Example 3-16 Pd—Al₂O₃ 19.6 82 Example 3-17 Ir—Al₂O₃ 19.2 80 Example 3-18Ag—Al₂O₃ 19.4 79 Example 3-19 Cu—Al₂O₃ 19.5 82 Example 3-20 Ru—Al₂O₃19.7 75 Example 3-21 Rh—Al₂O₃ 19.4 78 Example 3-22 Pt—TiO 19.6 73Example 3-23 Pd—TiO 19.9 80 Example 3-24 Ir—TiO 19.3 78 Example 3-25Ag—TiO 19.5 74 Example 3-26 Cu—TiO 19.0 79 Example 3-27 Ru—TiO 20.0 76Example 3-28 Rh—TiO 19.8 78 Example 3-29 Pt—TiC 19.3 79 Example 3-30Pd—TiC 19.3 75 Example 3-31 Ir—TiC 19.5 77 Example 3-32 Ag—TiC 19.0 78Example 3-33 Cu—TiC 18.9 74 Example 3-34 Ru—TiC 18.9 74 Example 3-35Rh—TiC 18.9 80 Example 3-36 Pt—TaC 19.0 79 Example 3-37 Pd—TaC 19.0 77Example 3-38 Ir—TaC 19.3 73 Example 3-39 Ag—TaC 19.2 74 Example 3-40Cu—TaC 19.2 78 Example 3-41 Ru—TaC 19.1 75 Example 3-42 Rh—TaC 19.1 79

Increase of SNR_(m) was found for magnetic recording medium disposing anunder-layer composite with chemical compound under the CoCrPt—SiO₂magnetic recording-layer. Similar results were found for magneticrecording medium having other magnetic recording-layer. Each magneticrecording-layer and under-layer show granular structure, and themagnetic crystalline grains show essentially tetragonal arrangement.

EXAMPLE 4

2.5 inch hard disk shaped nonmagnetic glass substrates were prepared andtraced the procedure of Example 3 except that one orientation controllayer was disposed between soft magnetic under-layer and grain diametercontrol layer. Then various magnetic recording media were obtained. Asthe orientation control layer, 5 nm NiAl-layer was deposited in 0.7 PaAratmosphere preparing and using NiAl targets. In addition, magneticrecording media having orientation control layer of MgO, NiO, MnAl, Ge,Si, and TiN, respectively, are fabricated.

Table 4 shows recording and reproducing characteristics of each magneticrecording medium having CoCrPt—SiO₂ magnetic recording-layer and Pt—SiO₂under-layer. TABLE 4 Orientation signal to Half width Controlling noiseratio DPW₅₀ Under layer SNRm (dB) (nm) Example 4-1 none 19.8 77 Example4-2 NiAl 20.5 76 Example 4-3 MgO 20.3 75 Example 4-4 NiO 20.0 76 Example4-5 MnAl 20.3 77 Example 4-6 Si 20.0 73 Example 4-7 Ge 20.1 76 Example4-8 TiN 20.4 76

As shown in Table 4, SNR_(m) increases further by disposing theorientation control layer. Similar results were found for magneticrecording medium having other combination of under-layer and magneticrecording-layer.

Although the prevent invention has been shown and described with respectto best mode embodiments thereof, it should be understood by thoseskilled in art that the foregoing and various other changes in the formand detail without departing from the spirit and scope of the presentinvention.

1. A method for producing magnetic recording medium, comprising: aprocess for forming a grain diameter control layer comprising Cucrystalline grains on a substrate; a process for forming a depositedlayer of nitrogen atoms depositing nitrogen on the grain diametercontrol under-layer surface; and a process for forming a magneticrecording-layer on the substrate having the nitrogen-layer depositedgrain diameter control under-layer.
 2. The method for producing magneticrecording medium as set forth in claim 1, wherein the nitrogen atoms aredeposited in an average areal density range from 1×10¹³ atoms/cm² to1×10¹⁵ atoms/cm² on the grain diameter control under-layer surface atthe process for forming a deposited layer of nitrogen atoms.
 3. Themethod for producing magnetic recording medium as set forth in claim 1,wherein the grain diameter control under-layer comprising 50 nm orlarger Cu crystalline grains is formed at the process for forming agrain diameter control under-layer, and the nitrogen atoms are depositedon the grain diameter control under-layer surface at the process forforming a deposited layer of nitrogen atoms.
 4. The method for producingmagnetic recording medium as set forth in claim 1, wherein the Cucrystalline grains of the grain diameter control under-layer orienting(100) planes of the crystalline grains parallel to the substrate surfaceis formed at the process for forming a grain diameter control layer. 5.The method for producing magnetic recording medium as set forth in claim4, wherein the magnetic crystalline grains are arranged essentially in aform of tetragonal lattice structure in the magnetic recording-layerplane at the process of forming a magnetic recording-layer.
 6. Themethod for producing magnetic recording medium as set forth in claim 1,wherein the magnetic crystalline grains in the magnetic recording-layerare formed in an average areal density range from 1×10¹² grains/cm² to8×10¹² grains/cm² at the process for forming a magnetic recording-layer.